It is generally known that acetylenically unsaturated compounds can be hydrocarboxylated by reaction with carbon monoxide and a carboxylic acid to yield carboxylic anhydrides.
According to a process known from U.S. Pat. No. 3,641,137 a catalytic system for such reactions is formed by combining a compound of divalent palladium with an organic phosphine, in a quantity of organic phosphine generally in excess (for example 10-300%) of that stoichiometrically required to form a complex with the palladium metal. A ratio mol of organic phosphine to gramatom of divalent palladium of 4 was reported in that patent for the two examples of this known process, corresponding to an excess of 100%. This known process has a very low reaction rate, which renders it unattractive for use on a commercial scale.
Investigations with increased molar ratio of organic phosphine to gramatom of divalent palladium, to a value in excess of 300%, have still shown a low rate of reaction.